.xuanfeng
{
    position: absolute;
}

.web_bg{
    background-image: url("http://img.zcool.cn/community/01367e566c13626ac7256b29413644.gif");
    position:fixed;
    top: 0;
    left: 0;
    width:100%;
    height:100%;
    min-width: 1000px;
    z-index:-10;
    zoom: 1;
    background-color: #fff;
    background-repeat: no-repeat;
    background-size: cover;
    -webkit-background-size: cover;
    -o-background-size: cover;
    background-position: center 0;
  }